There has been considerable activity within recent years toward the development of leak-proof valves for controlling flow of corrosive fluids under high pressures and temperatures. In designing a valve for this purpose, it is important not only to provide an effective seal, but also to offer minimal resistance to valve rotation.
Since a greater number of process lines are used for high pressure fluids rather than vacuums, a correspondingly greater amount of attention has been devoted to providing effective seals for valves in high pressures lines. Consequently, many widely used valves today are relatively ineffective when used in a high vacuum application.
A plug valve has a plug portion which is rotatably fitted within a valve body. The plug portion of the valve is joined by a stem or shaft portion which extends out of the valve body to interact with an actuator and transmit torque to the plug portion. This torque is used to rotate the plug portion within the valve body and move a passageway through the plug portion of the valve in and out of registry with a flow passage extending through the valve body.
A number of different types of top seals have been used in the past to seal the rotary stem or shaft of the valve exterior. In one highly successful approach, a delta ring bearing has been circumscribed about the stem or shaft with an interference fit. A diaphragm with a central opening for the stem or shaft has been fitted about the stem in overlaying relationship to the delta ring. This type of arrangement is illustrated in U.S. Pat. No. 3,703,910 to Smith.
Another successful top seal uses a diaphragm with a reverse lip which engages and extends along the stem's periphery. In this sealing arrangement, the diaphragm has a central opening through which the stem extends. The radial intermost portion of the diaphragm in engagement with the stem is folded so as to orient the internal periphery of the opening to extend axially along the stem. In this arrangement, the opening in the diaphragm for the stem is in substantially perpendicular relationship to the outer and intermediate portions of the diaphragm.
The second mentioned seal discussed above, is not satisfactory for vacuum service as vacuum within the valve tends to collapse the diaphragm, pulling it away from the stem and diminishing the sealing relationship thereto.
Applicant has developed a seal which is similar in many respects to both of the seals discussed above, but which makes important improvements which greatly enhance the sealing capabilities. The seal of the present application is highly effective in either positive or negative pressure situations.
Accordingly, it is an object of the present invention to provide a seal for a plug valve which is highly effective in both pressure and vacuum applications.
It is another object of the present invention to provide a seal for a plug valve which offers minimal resistance to valve rotation while sealing against both positive and negative pressure differentials.
These and other objects and advantages of the invention will be more readily apparent upon reading the following detailed description and upon reference to the accompanying drawings.